1841 Router shows line protocol is down when connected to the ISP Modem

I have a problem wherein when i put the Cisco Router 1841 between the Firewall and the ISP Modem, I get line protocol is down for both the fast ethernet interfaces.

Whereas when I bring router outside to test from some other interface, the router interfaces work perfectly fine. The addresses are fine and the cable is fine too. This Router has to be swapped with a another Router that is in operation which works fine when put between the ISP Modem and Firewall.

Really appreciate if someone could give any insights as to where I am wrong here.

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I am seeing the Interface configured as Duplex and Speed as Auto. Might be that cause of this problem. Please change the Duplex setting to auto to try full or half and also speed 100 or 10 . try this combination.